As shown in FIG. 1, a metal organic chemical vapor deposition (MOCVD) reactor includes a reaction chamber 100, in which there is a tray 14 and several substrates 15 to be processed are fixed on the tray 14. There is a rotation shaft 24 at the center below the tray 14, driving the tray 14 at high speed during the reaction. There is a heater 12 below the tray 14, which heats the tray 14 to appropriate high temperature that is about 1000° C. normally to facilitate the crystallization of the GaN crystalline material. A gas showerhead 21 is positioned opposite to the tray 14 in the reaction chamber 100. The gas showerhead 21 includes multiple gas inlet channels that are separated. The first group of gas channels is connected to the first reaction gas source 41 through gas pipeline 43. The second group of gas channels is connected to the second gas source 42 through the second gas pipeline 44. In the gas showerhead 21, the third group of gas channels can be set between the first and second groups of channels to isolate different reaction gases. The lower part of the gas showerhead 21 further includes cooling liquid pipeline that is connected to the cooling liquid source 50 through the cooling liquid supply pipeline 51. The temperature of the gas showerhead can be controlled by controlling the temperature and flow rate of the cooling liquid outputted from the cooling liquid source, such as 50° C. A reactor liner 62 is positioned surrounding the reaction space between the gas showerhead and the tray. The upper part of the liner 62 further includes a driving mechanism 64 which is used to drive the liner 62 to move up and down. When the liner 62 is at a higher position, it can shield the tray entry port (not shown in the figure) on the sidewall of the reaction chamber 100, so as to reduce the non-uniformity caused by the tray entry port and improve the uniformity of the gas flow and temperature. When the process on the tray is completed, the tray will be removed out of the reaction chamber. The liner 62 is driven to move downward so as to make the tray 14 pass through the tray entry port on the sidewall 100. A base is set below the tray 14. The base further includes a sidewall 16 which surrounds the rotation shaft 24 and the heater 12 so as to shield the heat inside the base and the contaminants outside the base. The lower part of the reaction chamber further includes an exhaust area 34. The by-products and waste gases after the reaction will be delivered to the gas pump 36 through pipelines to discharge the by-products and waste gases from the reaction chamber and to control the gas flow and pressure in the reaction chamber. There is a ring shaped gas baffle 30 horizontally set between the exhaust area 34 and the reaction area. The inner side of the gas baffle 30 is fixed on the outer side of the base, and the other side is fixed on the inner wall of the reaction chamber 100. There are one or more gas openings 31 on the ring gas baffle 30, which can be annular grooves or gas holes uniformly distributed on the ring shaped gas baffle 30. The flow rate and distributions of the gases in the reaction area can be controlled by setting the size of the gas openings 31. The cooling liquid supply system 51 can also supply cooling liquid to the liner 62 and the sidewall of the reaction chamber 100 to control the temperature of such components.
In the prior art, during the reaction, the reaction gases will produce GaN or other nitrides, meanwhile, the reaction gas trimethylgallium (TMG) will produce a great amount of organic matters at high temperature. Such solid products can form compact semiconductor crystals on the tray 14 and substrate 15 at high temperature, but loose depositions will deposit on the reactor components with low temperature such as the liner 62, the inner wall of the reaction chamber 100 or the gas showerhead 21, which may form flaky contaminants or depositions after a long time. These flaky contaminants or depositions will peel off and then fall onto the gas baffle 30 down below. Some flaky contaminants with large sizes will block the gas openings 31. Once the exhaust ports 31 are blocked, the distribution of the reaction gases will not be uniform and the structure of the crystals grown on the substrates will not be uniform, which will significantly influence the productivity and quality of the LED substrates.
To solve the above problems, the power must be turned off and the reaction chamber must be opened frequently to clean the depositions on the gas baffle 30, which may influence the productivity of the CVD apparatus. One of the prior arts discloses that a cleaning device can be installed on the liner 62. A cleaning apparatus is connected with and driven by the liner 62 to pass through the gas openings to break the depositions when the liner 62 is moving downward. However, such design also has disadvantages, since the liner 62 can only move up and down for one time after the completion of the whole reaction procedure and the duration of the reaction may be as long as several or dozens of hours, during such long procedure the opening 31 may be blocked and the opening can't be unblocked instantly. This design cannot solve such problem. Therefore, a better cleaning device or cleaning method is required to ensure the long-term and effective cleaning of the exhaust ports of the CVD apparatus.